Archived

Avalanche Forecast

Feb 20th, 2019–Feb 21st, 2019

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

1: Low

The avalanche danger rating at treeline will be low

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: South Rockies.

Rider triggered avalanches on persistent weak layers remains possible at lower elevations. Terrain like cutblocks, steep forest openings and gullies are still suspect. At upper elevations wind slabs are the primary avalanche concern.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Trace snowfall amounts, moderate north east winds, alpine temperatures -17 C.THURSDAY: Mix of sun and cloud, east winds switching to south west mid-day, alpine temperatures -12 C.FRIDAY: Increasing cloud, light snow possible, west winds, alpine temperatures -10 C.SATURDAY: Light accumulations possible, light east winds, alpine temperatures -11 C.

Avalanche Summary

There was evidence of many small to large (size 1 to 2) natural wind slab avalanches in the region over the last three days. More recently ski cutting has produced whumpfing, cracking and small avalanches over convex features at various elevations. Sled cuts were still producing slab avalanches at lower elevations on cut banks and cutblock type terrain on the last South Rockies Field Team trip to this region. There was also evidence of 40 cm slabs scrubbing to ground in very shallow snowpack areas.

Snowpack Summary

Recent incremental snowfalls total 20-30 cm, with the highest amounts in the south of the region. The snow likely has slab properties where it has been wind affected at higher elevations and open areas. It could be more loose in sheltered areas.The mid-January layer weak layer is buried around 50 to 80 cm. The weak layer is surface hoar on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m but has been found up to 2200 m. In some areas the weak layer is made up of sugary faceted crystals over old wind slab or a crust. Snowpack test results suggest that this layer may still be triggered by humans.The middle of the snowpack is generally consolidated. The bottom half of the snowpack is unconsolidated and composed of weak and sugary faceted grains. There is potential for shallower avalanches to step down to these deeper weak layers.

Avalanche Problems

Wind Slabs

Use added caution in lee terrain features near ridges, as winds have formed stiff deposits. The wind was first from the west and more recently from the northeast, so all lee features are suspect.

Use caution in freshly wind-loaded features, especially near ridge crests and in steep terrain.If triggered, wind slabs may step down to deeper layers resulting in large avalanches.Keep an eye out for reverse loading created by an upslope storm.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 2

Persistent Slabs

A weak layer of surface hoar is buried around 50 to 80 cm, which is best preserved in shaded and sheltered areas between 1600 m and 1900 m.

Use added caution in open terrain features such as cutblocks, gullies and cutbanks.Be aware of the potential for wide propagation.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood: Possible

Expected Size: 1 - 2.5